Caustic Jail

A sphere of silvery liquid blooms at a point within range, filling a 20 foot radius sphere entirely.

Huge or smaller creatures caught in this area when it appears are fully enveloped in the sphere, though creatures within 5 feet of the edge may make a Strength saving throw, ejecting themselves from the sphere on a success. Creatures contained with in the sphere are restrained and can make a Strength saving throw at the beginning of their turn to be able to swim through the sphere, through which each foot moved takes 5 feet.

Any creature whose dimensions exceed the sphere's succeeds on the Strength saving throw automatically. It can fit up to eight medium or small creatures, two large creatures, or one huge creature. If these limits are exceeded, a random creature is pushed out, exiting prone next to the sphere.

As an action on subsequent turns you can move the sphere up to 30 feet, carrying its restrained victims with it. If you ram a creature with the sphere it must make the saving throw or be restrained within it. If the sphere encounters a significant decline in elevation (i.e. a cliff) it descends at 60 feet per round, coming a gentle stop hovering 1 foot above the ground.

Creatures that begin their turn in the area of the sphere suffer 12d4 acid damage, even if they are not restrained. For every foot a creature swims through the sphere it takes an additional 1d4 acid damage. After exiting the sphere, a creature takes 6d4 acid damage at the start of its next turn.

When the spell ends, the sphere falls to the ground and extinguishes all normal flames within 30 feet of it. Any creature restrained by the sphere is knocked prone in the space where it falls. The acid then vanishes.